Lab-On-Chip (LoC) systems are designed to carry out one or more steps of a chemical or biological process, often in a disposable sample cartridge or a silicon chip that is controlled and read by a reusable, portable device. For example, LoC systems are widely used to perform analyses such as PCR amplification, antibody testing, biochemical reactions, and microarray-based DNA, RNA, or protein analyses.
Lab-On-Chip systems are proving to be effective in a wide range of practical situations and provide several advantages over conventional bench top methodologies. For example, LoC systems allow completely automated and repeatable processes, minimize sample size, ensure accurate control of process parameters, especially temperature, and the single use sample cartridges minimize contamination and provide for convenient disposal. Moreover, the LoC cartridges and the device that controls the process parameters and reads the results are portable. Thus, analyses can be carried out in the field, immediately after sample collection, and problems of sample preservation are eliminated and results are obtained much more quickly.
However, certain issues related to use of LoC systems still need to be satisfactorily addressed—in particular, fluid loss due to evaporation. Samples processed in LoC systems are usually water based, and thermal cycles raise the temperature and favor evaporation. Since the volumes involved in LoC reactions are typically very small, evaporation can easily affect the concentration of reagents and alter results.
LoC inlets can be sealed by applying a rigid cap once the chip or cartridge has been filled with sample. This solution is not optimal, however, because pressure dramatically increases on heating, possibly affecting the reaction or breaking the cap or even the entire chip.
Integrated membrane valves or bonded elastic caps can cope with pressure increases, but manufacturing and use of LoC cartridges that incorporate such solutions are more complex and costly.
An alternative solution, used historically in bench top PCR reactions, requires the addition of a mineral oil layer on top of the sample. Mineral oil has a lower density than water, forms a film on the surface of the sample and prevents its evaporation. At the same time, the thin film allows expansion of the sample caused by thermal cycling, so that pressure is sufficiently stable to preserve both the reaction conditions and chip integrity.
However, addition of mineral oil must be carried out manually after loading the sample into the chip, and the risk of sample contamination is considerable and preferably avoided. Also, since there is no proper cap, the sample may spill during movement, exposing laboratory technicians and the laboratory site to dangerous pathogens or toxic reagents.
The object of this invention, therefore, is to provide a self-sealing microreactor and a method for carrying out a reaction that is free from the above described limitations.